Method of pretreating and phosphatizing a metal surface for siccative coatings



United States Patent Oflice 3,118,793 Patented Jan. 21, 1964 METHOD OFPRETREATING AND PHOSPHATIZ- INC A METAL SURFACE FOR SICCATIVE COATINGS 3James E. Maloney, Oak Park, and Wilford H. Ross, Jr.,

Dearborn, Mich., assignors to Detrex Chemical Industries, Inc., Detroit,Mich., a corporation of Michigan No Drawing. Filed Dec. 6, 1960, Ser.No. 13,999 18 Claims. (Cl. 148--6.15)

This invention relates to the protective coating of metals, and moreparticularly to a composition and method for improving the corrosionresistance of ferrous metal surfaces which are treated with phosphatecoating compositions, and subsequently have applied thereto a coating ofsiccative material. This is a contiuuation-in-part of our copendingapplication. Serial No. 860,332, filed December 18, 1959, now abandoned.

It has been recognized for some time that the corrosion resistance ofmetals such as iron and steel may be increased materially by subjectingthe metal to preliminary treatment with phosphate coating compositions.Such treatment is intended to deposit an integral adherent phosphatecoating on the surface of the metal, which coating tends to preventcorrosion by resisting the action of moisture or other oxidizinginfluences.

In the metal finishing industry where ferrous metals are usuallyphosphate coated as above described prior to the application of asiccativc coating. such as varnish, lacquer, paint. japan or the like, amajdr problem exists in that a certain percentage of the metal has asurface which is passive in the respective that it will not accept aphosphate coating suitable for the application of an overlying siccativecoating. A further percentage of such metal has surface characteristicswhich will admit of the acceptance of a phosphate coating suitable forthe application of a subsequently applied siccative coating, but thecorrosion resistance of the phosphate siccative coating combination isinadequate and far below the average result desired upon the subjectionof such steel coated surfaces to a standard accelerated salt spray test.

it is an object of this invention to provide a composition and methodfor pretreating ferrous metal surfaces prior to the formation thereon ofan integral adherent metal phosphate coating and the subsequentapplication thereto of a siccative material which will result in animproved and uniform corrosion resistance of such coated metal surfaces.i

lt is another object (if the irivention to provide such a compositionand method which results in a greatly increased corrosion resistance asmeasured by the standard accelerated salt spray test.

It is a further object of this invention to provide a composition andmethod whereby light rust and scale may be removed from metal surfacessimultaneously with the pre-treatmcnt of said surfaces in accordancewith this invention.

Further objects and advantages of the composition and method of thisinvention will become apparent from the reading of the followingdescription and claims.

It has now been discovered that the application of solutions oremulsions containing certain substituted short chain mono-carboxylicacids to ferrous metal surfaces such as iron and steel activates suchmetal surfaces, renders them uniformly receptive to the formationthereon of a moderately refined, uniform and adherent phosphate coatingwhich when subsequently treated with a siccative coating gives saltspray accelerated corrosion results which are superior to the resultsobtained in the past by any other known method of treatment. Among thoseacids which are suitable for use in accordance with the method andcompositions of this invention are the ill hydroxy-substitutedmono-carboxylic acids such as glycoiic, lactic, hydroxy propionic,hydroxy butyric, hydroxy valeric, hydroxy caproic and glyceric (2,3,dihydroxy propionic) acids; diglycolic acid; thioglycolic andthiodiglycolic acids; chloro-substituted mono-carboxylic acids such asmonochloroacetic acid, dichloroacetic acid, trichloroacetic acid anda-chloropropionic acid; as well as aminoacetic acid and cyanoaceticacid.

It has additionally been discovered that the composition and processwhen used in accordance with this invention will remove light rust andscale from ferrous metal surfaces simultaneously with theabove-described activation of said surface.

Subsequent to the preliminary activation treatment utilizing thecomposition and process of this invention, the treated metal surface isphosphate coated by the application thereto of conventional phosphatecoating chemicals which may be selected from a wide variety ofwell-known solutions which produce fine grain integral adherentphosphate coatings on the metal. One such coating composition has as itsessential ingredients, zinc dihydrogen phosphate, a nitrate and freephosphoric acid. Similarly other dihydrogen phosphates such as manganesemay be utilized. Also, instead of using nitrates as an accelerator,other substances such as chlorates may be used. Activators such asnickel. copper, cobalt, fluorides. etc., may be at times usefullyemployed. The phosphate coating chemicals as well as the methods bywhich they are applied are Well-known in the phosphating art. Among theconventional methods for applying such compositions are dipping,spraying or the like.

It is also preferable when applying the pre-treating compositions inaccordance with the method of this inyention to include in thecomposition a solvent, detergent, wetting agent, or other surfactantmaterial. Organic detergents having desirable wetting and emulsifyingpowers for example are sodium alkyl sulfates, such as sodium allylsulfate; sulfonated hydrocarbons such as alkyl naphthalene sulfonicacid; and certain non-ionic" detergents such as the polyethylene glycolderivatives including among others the alkyl aryl polyether alcohols. Itwill be readily appreciated that the surfactant chosen must be one ofthose compatible with acid systems. It is not indispensable to theeffective utilization of the composition and process of this inventionthat any surfactant be utilized, and other chemicals in addition tothose mentioned may be added to the composition of this invention, wheresuch chemicals tend to improve the performance of the system withoutaffecting or inhibiting the subsequently applied coating materials.

The glycolic acid solutions which are effective in accordance with thisinvention may have the following range of compositions:

. Percent by weight of solution Glycolie acid (hydroxy acetic acid) 1-70Solvent 30-99 The diglycolic acid solutions which are effective inaccordance with this invention may have the following range ofcompositions:

Percent by weight of solution Diglycolic acid (a,a'-dicarboxyl dimethylether) 5-40 Solvent 60-95 The above compositions may have suitablyincluded therewith an appropriate amount of solvent, detergent, wettingagent, or other surfactant. The above solutions may be utilized asconcentrated solutions although all but the most dilute are moreeconomically further diluted with a solvent in the proportions of from1:2 to 1:10 and are effective as so diluted. It is to be understood thatthe term solvent" includes but is not limited to water. For example,mineral spirits may effectively be used as such a solvent. The mineralspirits solution may be removed lrum the treated surface by wateroverflow as a consequence of its ready cmulsification with water. Themineral spirits solution above may also be used as the basis for anemulsion by substituting a blend of alkylaryl polyether alcohols andorganic sulfonates for the dioctyl ester of sodium sulfosuccinic acid. Asuitable concentration would then be a 30% emulsion in water.

The following examples will indicate the application of the compositionand method of this invention; however, it will be obvious to one skilledin the art that various modifications may be made without departing fromthe composition and process of this invention as hereinafter claimed.

Example 1 A slightly rusted steel sheet was immersed for thirty secondsin an aqueous soluti n of glycolic acid containing 25% by weightglycolic acid per total weight of the solution. The sheet was removedfrom the glycolic acid and rinsed with water for thirty seconds. Thetreated sheet was then conventionally treated with phosphate coatingchemicals by immersion in a cleaning solution for sixty seconds. rinsingwith water for thirty seconds. immersion in a rim: dihydrogen phosphatesolution for sixty seconds, rinsing with water for thirty seconds, andfinally rinsing with a chromic rinse for thirty seconds. A siccativecoating consisting of a gilsonite primer and a gilsonite top coat wasthen applied to the treated sheet and dried. The coated sheet was thensubjected sheet and dried. The coated sheet was then subjected to anaccelerated salt spray test for a period of 336 hours, at the end ofwhich time no failures of the siccative coating were observed.

Example 2 t Example 3 A group of lightly rusted steel test panels waspretreated by wiping with a solution of glycolic acid in mineralspirits. The solution used had the following composition; parts beingexpressed as percent by weight r of the total weight of solution:

Mineral spirits 70.0 Dioctyl ester of sodium sulfosuceinic acid 13.0line oil 7.0 (jlycolic acid (7()%) 10.0

Good rust removal was observed as a result of the wipe. The panels werethen rinsed with water for thirty second. The treated panels were thenconveniently treated with phosphate coating chemicals and painted as inExample 1. A group of control panels were treated in the same way exceptthat a plain mineral spirits wipe was substituted for the wipe with themineral spirits solution of glycolic acid. The panels were then allsubjected to a 336 hour accelerated salt spray test. Those panels whichhad been pretreated showed no failures and a total paint crecpage from ascore line of A: to 7 inch. The control panels showed 4/; total failuresand total paint creepage from a score line of A to /2 inch (ignoring thetotal failures).

Example 4 A group of lightly rusted steel test panels was pretreated byspraying for one minute at 80 F. with a 5% solution of a compositionmade up as follows; parts till being expressed as percent by weight ofthe total of solution:

weight A further group of steel test panels was pretreated by wiping forone minute with a 25% solution of the above composition. Good rustremoval was observed as a result of the acid wipes.

A further group of steel panels was treated only by wiping withkerosene.

All panels were then rinsed with water for thirty seeonds and thenconventionally treated with phosphate coating chemicals and painted asin Example 1.

The panels were then all subjected to a 336 hour at:- celerated saltspray test. All of the pretreated panels showed no failures and a totalpaint creepage from a score line of'll to inch. The control panelsshowed total failures and total paint ereepage from a score line of A to/2 inch (ignoring the total failures).

Example 5 A group of lightly rusted steel test panels was pretreated bywiping with a solution of diglycolic acid. The solution used had thefollowing composition; parts being expressed as percent by weight of thetotal weight of solution:

Diglycolie acid 36.0 \Vater 59.5 Alkylpolyether alcohol 4.5

The time required for removal of light rust was longer Example 6 A groupof lightly rusted steel test panels was pretreated by wiping with asolution of diglycolic acid. The solution used had the followingcomposition; parts being expressed as percent by weight of the totalweight of solution:

Diglycolic acid 25.0 Water 74.0 Alkylpolyether alcohol 1.0

Good rust removal was observed as a result of the wipe. The panels wererinsed with water and then conventionally treated with phosphate coatingchemicals as in Example 1. Two groups of control panels were treated inthe same way as the test panels except that the pretreatment withdiglycolie acid was omitted. The test panels had coating weights of470-490 mgm./ft. The control panels had coating weights of 470-550mgmJftF. A siceative coating consisting of a gilsonite primer and agilsonite top coat was then applied to all panels.

The coated and painted panels were then subjected to an accelerated saltspray test with the following results:

Test panels 288 hours, moderate blistering and total paint ereepage froma score line A; inch.

Control panels 120 hours, severe blistering and loss of adhesion over toof the total area.

Example 7 Six lightly rusted steel test panels were pretreated by wipingwith a solution of monochloroacetic acid having the followingcomposition. parts being expressed as percent by weight of the totalweight of solution:

Monochloroucetic acid I0 lsooctyl pheuoxy polyethanoxy ethanol c .5WillL'l' ...e a e 39.5

A further group of steel panels was given no pretreatment. Three of thetest pltnclswere then rinsed with water for thirty seconds, and three ofthe test panels were allowed to dry completely without a water rinse.All of the panels were then conventionally treated with phosphatecoating chemicals and painted as in Example I. The panels were then allsubjected to a 330 hour accelerated salt spray test. All of theuntreated panels were badly corroded, while the treated panels wererated as having fair to good corrosion resistance.

Example 8 Six lightly rusted sttel test panels were pretreated by wipingwith a solution of thioglycblic acid having the following composition.parts being expressed as percent by weight of the total weight ofsolution:

Thioglycolic acid 10.0 Isooctyl phenoxy polyethanoxy ethanol .5 Water89.5

A further group of steel panels was given no pretreatment. Three of thetest panels were then rinsed with water for thirty seconds. and three ofthe test panels were allowed to dry completely without a water rinse.All of the panels were then conventionally treated with phosphatecoating chemical and painted as in Example 1. The panels were then allsubjected to a 336 hours accelerated salt spray test. All of theuntreated panels were badly corroded, while treated panels were rated ashaving good corrosion resistance.

Example 9 Six lightly rusted steel test panels were pretreated by wipingwith a solution of thiodiglycolic acid having the following composition.parts being expressed as percent by weight of the total weight ofsolution:

Thiodiglycolic acid 10.0 lsooctyl phenoxy polyethanoxy ethanol .5 Watern 89.5

A further group of steel panels was given no pretreatment. Three of thetest panels were then rinsed with water for thirty secorr s. and threeof the test panels were allowed to dry completely without a water rinse.All of the panels were then conventionally treated with phosphatecoating chemicals and painted as in Example 1. The panels were then allsubjected to a 336 hour accelerated salt spray test. All of theuntreated panels were badly corroded. while the treated panels wererated as having fair to good corrosion resistance.

Example 10 Six lightly rusted steel test panels were pretreated bywiping with a solution of cyanoacetic acid having the followingcomposition, parts being expressed as percent by weight of the totalweight of solution:

Cyanoacetic acid 10.0 lsooctyl phenoxy polycthanoxy ethanol .5 Water89.5

A further group of steel panels was given no pretreatment. Three of thetest panels were then rinsed with water for thirty seconds. and three ofthe test panels were allowed to dr completely without a water rinse.

All of the panels were then conventionally treated with phosphatecoating Lltctltlcttls and painted as in Example The panels ere then allsubjected to :t 336 hour accelerated salt spray test. All of theuntreated panels were badly corroded, while the treated panels wererated as having fair to good corrosion resistance.

Example I I Six lightly rusted steel test panels were pretreated bywiping with a solution of lactic acid having the following composition,parts being expressed as percent by weight of the total weight ofsolution:

Lactic acid 10.0 lsooctyl phenoxy polyethanoxy ethanol .5 Water c- 89.5

A further group of steel panels was given no pretreatment. Three of thetest panels were then rinsed with water for thirty seconds, and three ofthe test panels were allowed to dry completely without a water rinse.All of the panels were then conventionally treated with phosphatecoating chemicals and painted as Example I. The panels were then allsubjected to a 336 hour accelerated salt spray test. All of theuntreated panels were badly corroded, while the treated panels wererated as having fair to excellent corrosion resistance.

While in the above examples, water is shown as the solvent component ofthe compositions utilized in accordance with this invention, asindicated above, mineral spirits may effectively be used as such asolvent. For example, VM & P naphtha, kerosene and xylene may besuitably incorporated together with the organic acids above disclosed.

Having thus described our invention, we claim:

1. In a method of producing a corrosion resistant coating on a terrousmetal surface including the steps of forming an integral adherent metalphosphate coating on said surface, and subsequently applying a coatingof siccative material upon said metal phosphate coated surface, theimprovement which comprises pretreating said metal surface prior to theformation of said metal phosphate coating by applying to said metal apretreating solution consisting essentially of a substituted short chainmonocarboxylic acid selected from the class consisting of glycolic,lactic, hydroxy propionic. hydroxy butyric, hydroxy valeric, hydroxycaproic, glyceric, diglycolic, thioglycolic, thiodiglycolic,monochloroacetic, dichloi'oacetic, trichloroacetic, ix-chloropropionic,aminoacetic and cyanoacetic acid. and a liquid diluent for said acid,said acid constituting at least about .001 percent by weight of saidsolution.

2. The method of claim 1 wherein said solution additionally contains acompatible surfactant.

3. The method of claim 1 wherein said acid is glycolic acid.

4. The method of claim I wherein said acid is lactic acid.

5. The method of claim propionic acid.

6. The method of claim butyric acid.

7. The method of claim valeric acid.

8. The method of claim caproic acid.

9. The method of claim acid.

10. The method of claim 1 wherein said acid is diglycolic acid.

ll. The method of claim I wherein said acid is thin glycolic acid.

l2. The method of claim 1 wherein said acid is thio diglycolic acid.

13. The method of claim 1 wherein said acid is monochloroacetic acid.

[4. The method of claim I wherein said acid is dichloroacetic acid.

l5. The method of claim 1 wherein said acid is tri chloroacetic acid.

16. The method of claim I wherein said acid is C!- chloropropionic acid.

1 wherein said acid is hydroxy 1 wherein said acid is hydroxy I whereinsaid acid is hydroxy l wherein said acid is hydroxy I wherein said acidis glyceric 17. The method of claim I wherein said acid is aminoaceticacid.

18. The method of claim 1 wherein said acid is cyanoacetic acid.

References Ciled in the file of this intent UNITED STATES PATENTS 8Johnson Aug. 28, I945 Alquisl et al May 29, 1951 Slreicher May 27, 1957Baecker et al Oct. 15, 1957 Blaser June 3, 1958 Davis Apr. 25, 1961FOREIGN PATENTS Great Britain June 15, 1955 UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No. 15, l l8,793 January 21. I964 JamesE. Maloney et al.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 1, line 32. for "respective" read respect column 3, line 30,strike out "sheet and dried, The coated sheet was then sub ected"; line59 for "second" read seconds I same column 3, same line 59 for"convenientl y read conventional ly Signed and sealed this 30th day ofJune 1964,

(SEAL) Attcst:

ERNEST W. SWIDER EDWARD J BRENNER Attesting Officer Commissioner ofPatent:-

1. IN A METHOD OF PRODUCING A CORROSION RESISTANT COATING ON A FERROUSMETAL SURFACE INCLUDING THE STEPS OF FORMING AN INTEGRAL ADHERENT METALPHOSPHATE COATING ON SAID SURFACE, AND SUBSEQUENTLY APPLYING A COATINGOF SICCATIVE MATERIAL UPON SAID METAL PHOSPHATE COATED SURFACE, THEIMPROVEMENT WHICH COMPRISES PRETREATING SAID METAL SURFACE PRIOR TO THEFORMATION OF SAID METAL PHOSPHATE COATING BY APPLYING TO SAID METAL APRETREATING SOLUTION CONSISTING ESSENTIALLY OF A SUBSTITUTED SHORT CHAINMONOCARBOXYLIC ACID SELECTED FROM THE CLASS CONSISTING OF GLYCOLIC,LACTIC, HYDROXY PROPIONIC, HYDROXY BUTYRIC, HYDROXY VALERIC, HYDROXYCAPROIC, GLYCERIC, DIGLYCOLIC, THIOGLYCOLIC, THIODIGLYCOLIC,MONOCHLOROACETIC, DICHLOROACETIC, TRICHLOROACETIC, A-CHLOROPROPIONIC,AMINOACETIC AND CYANOACETIC ACID, AND A LIQUID DILUENT FOR SAID ACID,SAID ACID CONSTITUTING AT LEAST ABOUT .001 PERCENT BY WEIGHT OF SAIDSOLUTION.